1. Technical Field
This description pertains generally to energy storage, and more particularly to materials for use in energy storage devices.
2. Background Discussion
Commercialization of the first Li-ion batteries in 1991 was made possible by the so-called rocking technology, which utilized LiCoO2 and graphite electrodes. Twenty-four years later, graphite is still used as a negative electrode in the majority of Li-ion batteries. The success of graphitic carbon electrodes is attributed to its high electronic conductivity, low volume change during cycling and long cycle lifetime. However, its low coulombic efficiency, and relatively low gravimetric theoretical capacity limits the usage of graphite in Li-ion batteries for long range electric vehicles and miniaturized portable electronics devices. These new advanced applications require materials with higher energy storage densities than graphite can provide. Among alternative anode materials, tin is an attractive candidate for its high theoretical gravimetric Li storage capacity of 990 mAhg−1. In addition, Sn has high metallic electrical conductivity, which can lead to highly conductive composite electrodes. Unfortunately, as with many high-capacity anode materials, the alloying reaction of Sn with Li is associated with extreme volume changes (˜300%) between the initial and final states. This expansion is thought to be responsible for the electrode failure of bulk micrometer tin particles after just a few cycles. One significant failure mechanism is crack propagation and pulverization of the active electrode material leading to electronically isolated fragments that no longer contribute to the total capacity of the electrode.
The abovementioned cell failure and corresponding short battery lifetimes represent the main challenge in this field and has significantly delayed the development of high-performance Sn anodes for Li-ion batteries. Developing a high capacity nanostructured Sn anode with good cycle life still remains a major challenge. In fact, even small Sn nanocrystals have been shown to suffer from deleterious effects of extreme volume changes during cycling.
Previous studies have found that nanoporous tin (NP-Sn) having a nanowire-like ligament morphology does not exhibit long-term cyclability when used as anode material in Li-ion.